In a dual chamber operating mode, following an atrial event, whether the atrial event is a spontaneous (detected P wave) or a stimulated (application of an A pulse) depolarization, the implantable device monitors the ventricular activity and at the same time, starts counting a period called the “atrio-ventricular delay”, generally designated “AVD” or “DAV.” If, after the AVD period no spontaneous ventricular activity (detected R wave) has been detected, then the device triggers a stimulation of the ventricle (application of a V pulse).
It should be understood that, although the invention will be described in the context of an implantable pacemaker device that includes channels for stimulation of and sensing in the atrium and the ventricle, and that can operate at least in the conventional AAI and DDD pacing modes, it is not so limited and is more broadly applicable to implantable devices. Initially, the operating mode of the pacemaker is the AAI mode with monitoring of the ventricular activity. The control algorithm then looks for the presence or absence of ventricular activity, which in this case could allow a suspected atrioventricular block (AVB), with the potential to switch to the DDD mode, namely dual chamber stimulation with atrio-ventricular association, that is to say calculating and applying an AVD for the ventricular controlled stimulation. This mode is also called the “AAIsafeR” mode.
EP 0 488 904 A1 and its counterpart U.S. Pat. No. 5,318,594, and EP 1 346 750 A1 and its counterpart U.S. Pat. No. 7,164,507 (both assigned to ELA Medical), describe such implantable devices with AAI/DDD automatic mode switching. In any case, it is important to accurately define the AVD duration.
Indeed, from a cardiac mechanics viewpoint, the AVD must be sufficiently long to allow the atrium to contract completely and thereby empty the blood it contains into the ventricle, and the ventricular contraction ideally must therefore occur after the atrial contraction is fully finished. But the ventricular contraction should not occur too long after the atrium is emptied, because if too long the AVD might dissociate the atrio-ventricular system, with a risk of triggering retrograde conduction arrhythmias, or reducing the effectiveness of the haemodynamics of the cardiac cycle. As the atrial contraction ends the ventricular filling, the time between the end of this filling and the beginning of the ventricular emptying is a “dead” or “lost” time from an haemodynamics point of view.
It is therefore important to improve the adaptation of the AVD for each patient, so that the start of the ventricular emptying (caused by the stimulation of the ventricle) occurs immediately after the end of the filling of the ventricle by the atrium.
In most of the known implantable pacemaker type devices, the AVD is automatically adjusted according to the detected sinus frequency, with the AVD being able to take various values between a maximum value (corresponding to a base AVD) and a minimum value. The value of the AVD calculated from the sinus frequency is further increased by an additional period if the atrial event is a stimulated event, so as to compensate for the delay between the stimulation and the detection in the atrium.
The basic parameters of the automatic calculation of the AVD are programmed by the practitioner at the time of implantation or during follow-up visits of the patient. In some devices, the AVD may be automatically adjusted by the device after an analysis of the patient's heart rhythm over a long period of time.
However, the programming of these parameters does not take into account the haemodynamics reality of each patient, and, furthermore, do not allow a fine adjustment of the AVD. This is because the calculation of the AVD does not consider whether the atrial contraction was or was not entirely terminated before ventricular pacing had been triggered.
To address this difficulty, the WO 2005/089866 A1 proposes to detect the atrial contraction by an endocardiac acceleration signal delivered by an appropriate accelerometer sensor. Such a sensor may be present on the atrial lead or on another lead, said lead being placed with the sensor directly in the atrium or in another position suitable to detect the signal of endocardiac acceleration (EA) (known as the “EA signal”) representative of the contractions of the atrium.
In this alternate approach, the device, after atrial pacing, uses a functional signal—the EA signal—representative of the cardiac mechanics, instead of a signal originated by the electrical propagation of the depolarization wave. This mechanical EA signal can also be exploited as a complement to the electrical signal, as described in US2007/0179541 A1 which proposes to measure and analyze the delay between the electrical and mechanical detections of the atrial contraction.
The WO 2005/089866 A1 suggests, however, to use the EA signal for different purposes, such as an optimization of the AV period in the case of a dual chamber pacing, an optimization of the VV delay in the case of a biventricular pacing for a cardiac resynchronization therapy (CRT), a detection of the capture in a cardiac cavity, etc.
However, as compared to the electrical signal, the component of the EA signal corresponding to the mechanical activity of the atrium not only presents an amplitude much lower than the amplitude of the EA signal corresponding to the mechanical activity of the ventricle, but it also happens much earlier in time. This renders detection of the atrial component and its analysis much more difficult. This situation also is believed to be the reason why, until now, it has not been proposed to use any technique based on the analysis of the atrial component of the EA signal to obtain really exploitable results, despite the interest of obtaining a signal accurately corresponding to the mechanical activity of the heart.